EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 118 AM EST SAT FEB 14 2015 VALID 12Z TUE FEB 17 2015 - 12Z SAT FEB 21 2015 ...OVERVIEW... A STRONG CONSENSUS REMAINS WITH RESPECT TO THE MAINTENANCE OF A WEST COAST/ERN PAC MEAN RIDGE AND DEEP DOWNSTREAM TROUGH THAT SHOULD SUPPORT WARM TEMPS OVER THE WEST/ROCKIES AND BELOW TO MUCH BELOW NORMAL TEMPS OVER THE ERN HALF OF THE CONUS. AN EARLY PERIOD SYSTEM MAY ALSO GENERATE VARIOUS PCPN TYPES OVER THE PARTS OF THE EAST. ...GUIDANCE EVALUATION AND PREFERENCES... FOR THE SYSTEM LIFTING NEWD FROM THE SOUTHEAST DURING DAYS 3-4 TUE-WED... HOW MULTIPLE PIECES OF ENERGY IN DIFFERENT STREAMS INTERACT WILL DETERMINE THE ULTIMATE EVOLUTION OF LOW PRESSURE FCST TO TRACK NEAR/JUST OFFSHORE THE EAST COAST. SOME SUPPORTING ENERGY IS STILL NOT EXPECTED TO REACH WRN CANADA UNTIL SUN SO CONFIDENCE IN A PARTICULAR SCENARIO REMAINS TEMPERED TO SOME DEGREE. GUIDANCE TRENDS OVER THE PAST TWO DAYS HAVE TENDED TO BE TOWARD GREATER SUPPRESSION IN ASSOC WITH A FASTER/MORE SHEARED PRESENTATION OF SHRTWV ENERGY REACHING THE SRN ROCKIES/HIGH PLAINS AS OF EARLY TUE. ECMWF/ECMWF MEAN RUNS ALSO SEEM TO BE TRENDING FASTER IN A NOD TO THE GFS/GEFS MEAN. THE 18Z GFS HAD ADJUSTED A LITTLE WWD WITH THE SFC LOW TRACK. GIVEN THE UNCERTAINTIES ALOFT THERE IS CERTAINLY ROOM FOR A REVERSAL OF RECENT TRENDS BUT AT THIS TIME PREFER TO EMPHASIZE AN AVG OF THE 12Z GFS/18Z GEFS MEAN AND 12Z ECMWF/ECMWF MEAN. CONSULT THE MODEL DIAGNOSTIC DISCUSSION PMDHMD FOR THE LATEST INFO REGARDING 00Z MODEL DIFFS/PREFS THROUGH 12Z TUE. UPSTREAM FROM THIS ERN SYSTEM... FROM DAY 5 THU ONWARD THE 12Z/18Z GUIDANCE HAS MADE SOME ADJUSTMENTS WITH SHRTWV DETAILS ALOFT AND SEQUENCE OF SFC FRONT/TRAILING HIGH TRACK/PROGRESSION FROM CANADA INTO THE CNTRL-ERN CONUS. THERE IS SUFFICIENT AGREEMENT AMONG THE GEFS/ECMWF/CMC MEANS TO FOLLOW THIS TREND AS A MORE CONFIDENT SOLN RELATIVE TO OTHER ALTERNATIVES. THERE IS BETTER AGREEMENT VERSUS 24 HRS AGO WITH THE WAVY FRONT OVER THE NRN HALF OF THE HIGH PLAINS INTO MID-PERIOD. FROM THE ERN PAC INTO THE WEST... MOST OPERATIONAL RUNS APPEAR TO BE TRENDING TOWARD RECENT ENSEMBLE MEANS WHICH SIGNIFICANTLY FLATTEN ERN PAC TROUGH ENERGY AS IT HEADS INTO THE MEAN RIDGE AROUND WED-THU AND ONLY DEVELOP A LITTLE AMPLITUDE OVER THE WEST ONCE ENERGY REACHES INLAND. THE 12Z ECMWF IS NOW A RELATIVE EXTREME WITH ITS SHARP/AMPLIFIED SHRTWV REACHING THE WEST COAST DAY 5 THU. FOR DAYS 3-4 TUE-WED THE AFOREMENTIONED BLEND OF THE 12Z GFS/18Z GEFS MEAN AND 12Z ECMWF/ECMWF MEAN OFFERS A GOOD INTERMEDIATE EVOLUTION FOR THE SYSTEM AFFECTING THE EAST EARLY IN THE PERIOD AND REFLECTS THE MOST COMMON IDEAS OF GUIDANCE ELSEWHERE. BY DAYS 5-7 THU-SAT OPERATIONAL MODEL DETAILS DIVERGE ENOUGH... ESPECIALLY WITH THE 12Z ECMWF LOOKING LESS DESIRABLE OVER THE WEST... TO RECOMMEND A BLEND OF SIMILAR 18Z GEFS/12Z ECMWF MEAN SOLNS. ...SENSIBLE WEATHER HIGHLIGHTS... THERE IS STILL LOWER THAN DESIRED CONFIDENCE WITH THE NWWD EXTENT OF MSTR IN ASSOC WITH THE MIDWEEK SYSTEM AFFECTING PARTS OF THE EAST... BUT IN GENERAL THERE APPEARS TO BE DECENT POTENTIAL FOR SOME SNOW TO FALL IN THE NWRN PERIPHERY OF THE PCPN SHIELD AND SEPARATED FROM RAIN TO THE S/SE BY A ZONE OF WINTRY MIX/FREEZING PCPN. HIGHEST PROBABILITY FOR SNOW SHOULD EXTEND FROM PARTS OF THE MID ATLC INTO NEW ENGLAND. LOCALLY HVY RNFL IS PSBL IN THE WARM SECTOR OVER THE EXTREME SOUTH. VERY COLD TEMPS WILL BE THE PRIMARY FOCUS BEHIND THIS SYSTEM WITH SOME AREAS OVER THE EAST SEEING ONE OR MORE DAYS OF MINUS 15-30F ANOMALIES UNTIL SOME MODERATION OCCURS BY FRI-SAT. WITH THIS LATE PERIOD WARMUP THERE WILL ALSO BE AN INCREASE IN MSTR/PCPN FROM THE SERN PLAINS THROUGH THE OH VLY AS GULF INFLOW STRENGTHENS. OVER THE WEST... AS WEAKENING SHRTWV ENERGY PASSES AROUND/THROUGH THE WEST COAST MEAN RIDGE AND MODESTLY AMPLIFIES INLAND EXPECT A LITTLE LGT PCPN TO SPREAD FROM THE PAC NW SEWD ACROSS THE ROCKIES THU ONWARD. WARMEST TEMPS RELATIVE TO NORMAL SHOULD BE OVER THE GRTBASIN WITH SOME PLUS 15-20F ANOMALIES PSBL WED-FRI. RAUSCH